Ag/Cu-I mixed occupancy in the crystal structures of the copper(II) cyanoargentates Cu(NH3)(py)Ag3-xCux(CN)(5)center dot py

From pyridine and ammonia containing Cu-II solutions, to which K[Ag(CN)(2)] and in part KCu(CN)(2)/KCN has been added, we obtained single crystals of mixed-valent copper compounds of variable composition Cu(NH3)-(py)Ag3-xCux(CN)(5) . py. The phases corresponding to x = 0.39(1) (I) and to x = 1.243(6) (II) were characterized by X-ray structure analysis. They are isomorphous and crystallize with Z = 4 in the monoclinic space group P2(1)/c. The lattice constants for I [and II, resp.] are: a = 923.8(2) [901.4(2)], b = 1226.8(2) [1227.3(2)], c = 1809.8(4) [1783.5(2)] pm, beta = 91.41(3) [91.02(1)]degrees. The Cu-II cation shows trigonal bipyramidal [CuN5] coordination, with the neutral ligands in axial positions (mean value Cu-N for II: 201 pm), three N atoms of cyano bridges in equatorial ones (Cu-N: 206 pm). One of these bridges stems from a trigonal unit [AgCN(NC)(2)], the central atom of which is substituted by Cu-I to an extent of 39% in I, and completely in II. The two other bridges originate from two [Ag(CN)(2)](-) groups, of which the more bent one may be partially occupied by Cu-I as well (24% in II). The units mentioned are connected into meshes of elongated hexagons and further into puckered layers within the (010) plane, interpenetrating each other in pairs. A threedimensional linking of layers occurs by the trigonal Ag/Cu-I species forming centrosymmetric dimers, in which the metal coordination is completed to tetrahedral by a C-atom of the corresponding neighbouring group and short metal-metal distances of 279.1(3) pm in I and 264.1(1) pm in II appear. Details and relations are discussed.